Open cycle ammonia refrigeration system including a catalytic ammonia burner

ABSTRACT

This invention provides an open cycle refrigeration system wherein ammonia, supplied from a refillable storage tank, is employed as a refrigerant, and after serving as the refrigerant, is disposed of by dissociation and combustion. HaVing substantially no moving parts and requiring no source of power when in operation, the refrigeration system of the invention has low initial cost and requires little maintenance. As a result of these features, the refrigeration system is especially useful in providing in-transit refrigeration for perishable or frozen commodities.

United States Patent 1 1 3,685,310 Fischer 1 1 Aug. 22, 1972 [54] OPENCYCLE AMMONIA 2,120,166 6/1938 Tonken ..62/7 REFRIGERATION SYSTEM2,533,583 12/ 1950 Hopp; ..62/141 gigfgg A CATALYTIC AMMONIA FOREIGNPATENTS OR APPLICATIONS [72] Inventor: Harry C. Fischer, y 31 Oak, M d.469,753 9/ 1937 Great Britain ..162/7 [73] Assigneez' Allied ChemicalCorporation, New Primwy ll am J Wye York, NY. Att0rney-Stanley M.Teigland [21] Appl' 75,646 This invention provides an open cyclerefrigeration system wherein ammonia, supplied from a refillable 52 US.Cl. ..62/114, 62/7, 62/50, Storage tank, is employed as refrigerant, andafter 62/52, 62/141 serving as the refrigerant, is disposed of bydissocia- 51 Int. Cl ..F25b and Combustion Having Substantially moving[58] Field of Search ..62/7 50 52 141 114 parts and requiring no Sourceof Power when in opera tion, the refrigeration system of the inventionhas low [56] References Cited initial cost and requires littlemaintenance. As a result of these features, the refrigeration system isespecially UNITED STATES PATENTS useful in providing in-transitrefrigeration for perishable or frozen commodities. 1,774,820 9/1930WIllIams ..62/7

4/1933 Davisson ..62/7

17 Claims, 4 Drawing Figures PATENTEU AUG 2 2 I972 SHEET 2 OF 4INVENTOR. HARRY C. FISCHER $7241 Z ATTORNEY PATENTEDwszzmn 3.685310SHEET 3 OF 4 INVENTOR. HARRY C. FISCHER n M 17. 6 M

ATTORNEY PATENTED 3.685.310

SHEET u 0F 4 INVENTOR.

HARRY c. FISCHER Ian/, 77 4 11 ATTORNEY OPEN CYCLE AMMONIA REFRIGERATIONSYSTEM INCLUDING A CATALYTIC AMMONIA BURNER BACKGROUND OF THE INVENTIONThe in-transit refrigeration system most commonly used today is theconventional closed cycle system employing a compressor. Although thissystem is the most common, it has several drawbacks, including high iniltial cost and high operating cost resulting from required maintenanceand the need for an external source of power to drive the compressor. Toovercome these drawbacks, attempts have been made to develop betterintransit refrigeration systems. Many of these attempts have involvedopen cycle systems, i.e., systems wherein the refrigerant is consumedinstead of being recycled. One such attempt, involving the use ofammonia in an open cycle system, is described in US. Pat Nos. 2,504,689and 2,533,583. In the system described in these patents, ammonia, afterserving as the refrigerant, is absorbed by water. A major drawback ofthis system is that it requires bulky absorber tanks which must beperiodically drained of aqueous ammonia and recharged with fresh water.Disposing of the drained ammonia, which could be a pollutant, alsopresents a problem.

It is an object of this invention to provide a compact, efflcient andeconomical refrigeration system, especially for in-transit service.

SUMMARY OF THE INVENTION The refrigeration system of this inventioncomprises an open cycle ammonia refrigeration unit in combination withmeans for combusting the spent (vaporized) ammonia refrigerant. Thecombustion products, which contain no substantial amounts of harmfulsubstances, are discharged to the atmosphere. By disposing of the spentammonia in this manner, the invention overcomes the disadvantagesinherent in prior art open cycle ammonia refrigeration systems havingbulky absorber tanks which required draining and rechargingperiodically. The problem of disposing of the aqueous ammonia drainedfrom the absorber tanks is also eliminated by this invention.

The refrigeration unit of the system includes an evaporator whereinliquid ammonia is vaporized by absorbing heat from the surroundings ofthe evaporator, i.e., the compartment being refrigerated. Liquid ammoniais fed to the evaporator through a conduit from a storage tank which isnormally under autogenous pressure. The vaporized ammonia is conveyedfrom the evaporator through a conduit to means for combusting thevaporized ammonia. The refrigeration unit also includes' means forregulating the flow of ammonia through the system to control thetemperature of the compartment being refrigerated.

The vaporized ammonia can be burned directly in air. However, ammonia isdifficult to burn directly in air for several reasons. First, itrequires a very high ignition temperature 1562 F). Second, it has a slowflame propagation rate, which makes it necessary to maintain a low flowrate in order to prevent flameout. Hence, in order to initiate andmaintain direct combustion of ammonia in air, an auxiliary flame isnormally required. When an auxiliary flame is readily available, such asin a nearby furnace or under a boiler, the vaporized ammonia canconveniently be combusted by this means. Unfortunately, however, anauxiliary flame is not usually available, especially in transportvehicles.

The flammability of ammonia can be improved by adding to it a moreflammable gas, such as methane, acetylene, propane, or other petroleumgas. An advantage of this means for combusting the vaporized ammonia isthat it permits the use of conventional gas burners. However, a majordisadvantage of this means is that it involves the expense of supplyingthe more flammable gas.

The most effective gas to add to ammonia to improve its flammability ishydrogen, which can be generated by the catalytic dissociation ofammonia. Ammonia is dissociated into nitrogen and hydrogen in thepresence of known catalysts at temperatures of at least about 900F.Complete dissociation is not required because ammonia containing alittle as about 2 percent by weight of hydrogen has sufficientflammability to burn in air without assistance. By utilizing the heat ofcombustion to maintain the catalyst at operating temperature, thevaporized ammonia can be readily combusted in a unit which isself-sustaining when in operation.

Hence, a preferred means for combusting the vaporized ammonia is anammonia dissociator-burner comprising, within an insulated housing, aconduit containing an ammonia dissociation catalyst and having at itsterminus an aperture permitting dischargeand combustion of the partiallydissociated ammonia such that the heat of combustion maintains thecatalyst at a temperature at which ammonia is dissociated in thepresence of the catalyst.

Additional means for combusting the vaporized ammonia include internalcombustion engines which operate on either partially dissociated orundissociated ammonia as fuel. A principal advantage of such means isthat the engines provide a source of power for use with therefrigeration system, such as for circulating air in the refrigeratedcompartment, or for any other use.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an isometric view, with acutaway portion, of an embodiment of the refrigeration system of thisinvention as installed on a motor truck.

FIG. 2 is a schematic view depicting the embodiment of the inventionshown in FIG. 1.

FIG. 3 is a schematic view of another embodiment of the refrigerationsystem of this invention.

FIG. 4 is a schematic view of an ammonia dissociator-bumer.

DETAILED DESCRIPTION FIG. 1 illustrates a preferred embodiment of therefrigeration system as installed on a motor truck. A tank 10 forstoring liquid anhydrous ammonia refrigerant is secured to the undersideof a motor truck. The liquid ammonia flows from tank 10 through aconduit 11 to a surge tank 12. From surge tank 12 the liquid ammoniaflows through conduit 13 to an evaporator 14 wherein the ammonia changesto a vapor as it absorbs heat from the interior of the cargo compartmentof the truck. The vaporized ammonia leaves evaporator 14 through conduit15 and returns tosurge tank 12. Ammonia vapor flows from the surge tankthrough a network of conduits l6 and thermostatic throttling valve 17 toan ammonia dissociator-burner 18, wherein the ammonia vapor is partiallydissociated and burned, the combustion products being discharged to theatmosphere.

FIG. 2 shows the refrigeration system of FIG. 1 schematically in greaterdetail. The liquid ammonia storage tank 10 is equipped with a chargingport 19. A liquid level indicator 20 indicates the amount of liquidammonia in the tank. The tank 10 is constructed to withstand pressuresautogenously developed within the tank at ambient temperatures. Forexample, on a 100 F. day the pressure in the tank 10 would be about l97psig and on a F. day the pressure would be about 15.7 psig. Sufficientpressure is developed within tank to cause the liquid ammonia to flow tosurge tank 12.

Before entering surge tank 12, the liquid ammonia passes through a heatexchanger 21, wherein it is cooled by the ammonia vapor leaving thesurge tank 12.

The level of liquid ammonia in the surge tank 12 is controlled by a lowside float valve 22. In lieu of flat valve 22, a solenoid valve (notshown) actuated by a float switch (not shown) can be employed. A typicalfloat switch which may be used includes an interior float whichmagnetically operates an exterior switch.

The liquid ammonia flows by gravity from surge tank 12 through conduit13 to evaporator 14, which consists of roll-bond plates having internalpassages (formed in the roll-bond process) through which the ammoniaflows. Such plate type evaporators are readily available at low cost andare advantageous to use with refrigeration systems installed on smallertransport vehicles, such as local delivery trucks. The plates aremounted from the walls of the truck such that air convection around theplates can occur. Heat is absorbed from thecirculating air by theammonia as it changes from a liquid to a gas within the evaporator.

The vaporized. ammonia returns to surge tank 12 through the network ofconduits 15. The surge tank 12 permits separation of any liquid whichmight have been entrained with the returning vapor.

The pressure of ammonia in evaporator 14 is regulated by a thermostaticthrottling valve 17, which reacts to the temperature in the truck inresponse to a sensing bulb 23. The thermostatic throttling valve 17provides variable response to the refrigeration demands placed on thesystem. For example, a thermostatic throttling valve set at 32 F. willadjust the ammonia pressure to maintain a temperature of 32 F. withinthe truck.

When the doors of the truck are opened, the inrush of warm air strikingsensing bulb 23 will cause the thermostatic throttling valve 17 to open,thereby permitting a greater flow of ammonia, which results in alowering of the temperature in the evaporator 14. When the doors areclosed, thermostatic throttling valve 17 gradually closes as thetemperature in the truck drops to 32 F. As the valve closes, thepressure of the ammonia vapor increases and raises the temperature inevaporator 14. Inasmuch as the boiling point of ammonia at atmosphericpressure is 28 F, the thermostatic throttling valve 17 can be bypassedwhen it is desired to maintain the lowest possible temperature, such aswhen the cargo in the compartment is frozen food. Bypass valve 24permits the ammonia vapor to bypass the thermostatic throttling valve17.

A principal advantage of the refrigeration system of this invention isthat it permits variable response to refrigeration demands. Conventionalclosed cycle systems employing a compressor are not able to do sobecause such systems operate either at full capacity when the compressoris running or at no capacity when the compressor is not running. As aresult, such systems do not provide satisfactory refrigeration forperishable products, which should be kept at the lowest possibletemperature without being permitted to freeze. The refrigerationprovided by such systems is unsatisfactory because the temperature ofthe cooling coils (evaporator) goes much below freezing and usuallycauses the product loaded closest to the coils to freeze. In contrast,the refrigeration system of this invention provides immediate variableresponse (instead of merely starting and stopping) to meet therefrigeration requirements exactly without going below a settemperature.

After passing through or bypassing the thermostatic throttling valve 17,the ammonia vapor continues to flow through the network of conduits 16to an ammonia dissociator-burner 18. The ammonia vapor enters thedissociator-burner 18 at manifold 25 where the vapor is distributed to aplurality of conduits (catalyst tubes) 26 containing a catalyst 27 forpartially dissociating the ammonia vapor. Catalysts for the dissociationof ammonia are well known in the art. For reasons of economy andconvenience, iron, including activated iron promoted with AI O or othermetal oxides, such as A O, ZrO Cr O MgO, and CaO, is preferred. Ammoniadissociates in the presence of iron catalyst at temperatures above about900 F. A temperature range of from about 1,200 F. to about l,700 F. ispreferred.

The partially dissociated ammonia is discharged from each of theconduits 26 through apertures 28, which are located at the terminal endsof the conduits. Upon being discharged from conduits 26, the partiallydissociated ammonia is combusted in the presence of air such that theheat of combustion maintains the catalyst 27 at a temperature at whichammonia is dissociated in the presence of the catalyst. As shown in FIG.2, this can be achieved by arranging the conduits 26 vertically withcombustion occuring initially at the bottom of each of the conduits 26so that the hot combustion gases rise in heat exchange relationship withthe conduits 26. In order to conserve sufficient heat of combustion tomaintain the catalyst 27 at operating temperature, conduits 26 arecontained within an insulated housing 29 which defines a combustionchamber. The insulated housing 29 contains apertures 30 permitting airto mix with the discharged partially dissociated ammonia approximatelyin a stoichiometric ratio. The combustion gases are channeled throughthe insulated housing into an afterburner section 31 of thedissociator-burner 18. As the combustion gases are discharged to theatmosphere through openings 32 at the top of the afterburner section 31,they are diluted and cooled with air drawn in through grated openings33. By constructing the housing 29 and the afterburner section 31 in theshape of a tee, as shown in FIGS. 1 and 2, the refrigeration system canbe installed such that no part of it extends above the height of thetruck.

Upon start-up, the temperature of the catalyst 27 must be raised to thepoint where dissociation of the ammonia vapor occurs. When iron is usedas the catalyst, it is preferably raised to a temperature of at leastabout 1,000 F. The catalyst can be raised to this temperature by meansof electrical heating elements 34 embedded in the catalyst 26. Theelements 34 are heated by simply plugging electrical plug 35 into asuitable outlet while the truck is stationary. More simply, thetemperature of the catalyst can be raised to the desired temperature byapplying the flame of a portable torch to the conduit containing thecatalyst.

After catalyst 27 has been brought up to temperature, ammonia vapor ispermitted to flow through conduits 26 containing the catalyst 27. Ifdesired, the ammonia vapor employed during start-up can be takendirectly from the storage tank 10, in which case the vapor is permittedto flow through conduit 36 to dissociator-burner 18. Upon contactingcatalyst 27, the ammonia vapor is partially dissociated into nitrogenand hydrogen. Sufficient dissociation to generate at least 2 percenthydrogen by weight is required in order to produce satisfactorycombustion As the partially dissociated ammonia is discharged throughapertures 28, it is ignited by a continuous spark produced by anignition device 37. Ignition is only required during start-up. Insteadof producing a spark, the ignition device 37 could simply heat a wire tothe ignition temperature of the partially dissociated ammonia. The flameof a torch can also be used to start the burner.

After start-up, the dissociator-burner 18 is selfsustaining. When thedissociator-burner 18 is in selfsustaining operation, the optimumtemperature of the catalyst and the partially dissociated ammonia as itis discharged from conduits 26 is from about 1,200 F. to about 1,700 F.The optimum temperature within the dissociator-burner 18 at the walls ofthe combustion chamber is from about 1,500 F. to about l,900 F.

It would be ideal to operate the dissociator-burner 18 at a steady flowrate of ammonia, but in actual practice the flow rate fluctuates greatlyas it responds to the refrigeration demands placed on the system. Hence,the ammonia-dissociator 18 must be able to burn all ammonia delivered toit under conditions of both maximum and minimum flow; that is, thedissociatorburner 18 must be able to burn with substantially completecombustion all ammonia flowing at the maximum rate, yet combustion mustnot cease when ammonia is consumed at the minimum rate.

In the event the flow of ammonia through the refrigeration system fallsbelow the minimum amount necessary to sustain the flame in thedissociator-burner l8, sufficient ammonia to sustain the flame can besupplied directly from storage tank by placing a pressure regulatingvalve 38 in the conduit 36. By setting the valve 38 to open and maintaina minimum pressure in the conduit 16 connecting the surge tank 12 withthe dissociator-burner 18, when the pressure falls below the levelcorresponding to the minimum flow rate necessary to sustain the flame,valve 38 will open to maintain the minimum pressure necessary tomaintain the flame.

If, under conditions of maximum flow rate, all ammonia were allowed toflow through the conduits 26 containing catalyst 27, the result might bethat catalyst 27 would be cooled by the incoming vapor to the pointwhere the amount of hydrogen generated would be insufficient to sustaincombustion. To avoid this situation, ammonia in excess of the amountrequired to maintain the dissociator-burner 18 at the optimum operatingtemperatures is introduced directly into the dissociator-burner withoutcontacting catalyst 27. A bypass valve 39 diverts the flow of excessammonia from the conduits 26 containing the catalyst 27 to a conduit 40leading directly to the combustion chamber. The bypass valve 39 opens atthe pressure which corresponds to a flow rate at which ammonia isflowing in excess of that required to maintain the optimum operatingtemperature of catalyst 27. Since under optimum conditions thetemperature within the combustion chamber is above the ignitiontemperature of undissociated ammonia, the excess ammonia burns withoutdifficulty with the partially dissociated ammonia.

In order to maintain a steady uniform flow of ammonia to the catalysttubes 26, a gas regulator valve 41 is interposed in conduit 16. The gasregulator valve 41 limits the flow of ammonia vapor to the amountrequired to maintain the dissociator-burner 18 at the optimum operatingtemperatures. For example, if this amount corresponds to a pressure ofabout 5 inches of water (typical for a truck refrigeration system), thebypass valve 39 would be set to open at about 10 inches of water and thegas regulator valve 41 would be set to limit the downstream pressure toabout 5 inches of water.

During start-up, when the truck is warm, the rate of generation ofammonia vapor in the evaporator 14 might exceed the capacity of thedissociator-burner 18 to dispose of it without having flames appearoutside. This situation can be avoided by having a section of conduit 11be in the form of a capillary tube 42 which restricts the flow of liquidammonia to the rate at which the dissociator-burner 18 can convenientlydispose of the vapor generated from the liquid. A /5 inch OD capillarytube (0.042 inch ID) having a length of about 3 feet is suggested for atypical truck refrigeration system, but the size of the tubing could, ofcourse, be conveniently adjusted according to the capacity of theparticular dissociator-burner employed.

As supplied commercially, anhydrous ammonia may contain a minor amountof water and oil. The amount of oil seldom exceeds 30 parts per million,but depending on source, water may vary from 0.2 percent to severalpercent. This water and oil collect as a residue as the ammoniaevaporates in the evaporator 14. If permitted to accumulate, the waterand oil would eventually impair the operation of the refrigerationsystem. To prevent this from happening, the water and oil arecontinuously bled through conduit 43 to trap 44 located near the ammoniastorage tank 10 where they can be conveniently drained through valve 45located at the bottom of the trap Vent conduit 46 carries ammonia vaporfrom the trap to a connection in conduit 16 upstream from the throttlingvalve 17. The flow of water through the conduit 43 can be furtherlimited to a suitable rate of flow (corresponding to about the rate atwhich water is collected) by employing capillary tubing as the conduit43. The amount of ammonia which is lost through conduit 43 isnegligible.

In certain situations it may be more economical to recover the vaporizedammonia than to consume it. Such situations exist when refrigeration isrequired for extended periods of time during which the transport vehiclebearing the refrigeration system is stationary near an ammonia recoveryunit. For example, a local ice cream delivery truck which is on the roadonly during business hours usually requires refrigeration duringnonbusiness hours as well. Continuous refrigeration is required not onlyto have the truck ready for operation at the beginning of each day, butalso to avoid the problem of unloading and reloading the truck betweendelivery days: By conveyingthe vaporized ammonia to a recovery unitinstead of the dissociator-burner 18, when the truck is not on the road,the ammonia can be recovered for reuse. Another example involvesintermodal containers which are transported by ship or rail way(piggyback) as well as by trailer truck. When such containers are aboardship, at dockside, or at a terminal, they may similarly be connected toan ammonia recovery unit. Several transport units can be connected toone central recovery unit.

' By installing a manually operated on-off bypass valve in conduit 16,the ammonia vapor can be diverted from the dissociator-burner 18 to arecovery unit. The recovery unit liquefies the ammonia vapor and storesit for future use. Instead of being stored, however, the liquefiedammonia can be returned directly to the refrigeration system, in whichcase another manually operated on-off bypass valve is installed inconduit 11 to receive the liquefied ammonia.

Instead of connecting the refrigeration system to a recovery unit, thevaporized ammonia can be recovered by being condensed within the system,such as in the surge tank 12. For example, by condensing the.

ammonia vapor in surge tank 12 by means of cooling coils connected toanother refrigeration system, the ammonia can be recycled instead ofbeing consumed.

FIG. 3 schematically illustrates another embodiment of the refrigerationsystem of this invention. Liquid ammonia flows from the storage tankthrough a conduit 11 to a heat exchanger 47 wherein the liquid ammoniais cooled before passing through a thermostatic expansion valve 48 to anevaporator 14 wherein the ammonia changes to a vapor as it absorbs heatfrom the compartment being cooled. Upon leaving the evaporator 14, thevaporized ammonia flows through conduit 15 to the heat exchanger 47wherein the vapor absorbs heat from the incoming liquid ammonia. Fromthe heat exchanger 47 the ammonia vapor passes through a thermostaticthrottling valve 17 before entering the dissociatorburner 18. In orderto bring the dissociator-burner 18 up to operating temperature, and ifnecessary maintain it at operating temperature, liquefied petroleum (LP)gas is fed to the dissociator-burner 18 through conduit 49.

The liquid ammonia storage tank 10 is identical to the liquid ammoniastorage tank 10 shown in FIGS. 1 and 2. Liquid ammonia flows underautogenous pressure from the storage tank 10 through conduit 1 l to theheat exchanger 47. As the liquid ammonia passes through the heatexchanger 47, it is cooled by the vaporized ammonia coming from theevaporator 14 without coming in direct contact with the ammonia vapor.

The cooled liquid ammonia then passes through a thermostatic expansionvalve 48 which regulates the flow of liquid ammonia to the evaporator 14in response to the temperature of the vaporized ammonia as it leaves theevaporator 14. This temperature, which is measured by a sensing bulb 50,rises as the rate of flow of liquid ammonia to the evaporator 14 becomesinadequate; and in response to the higher temperature, the expansionvalve 48 opens a greater amount to increase the rate of flow.Conversely, as the temperature of the leaving refrigerant falls, theexpansion valve 48 gradually closes to decrease the rate of flow.

After passing through the thermostatic expansion valve 48, the ammoniaenters the evaporator 14 where it is vaporized as it absorbs heat fromthe interior of the refrigerated compartment. As depicted in FIG. 3, theevaporator 14 comprises conventional finned coils, which are normallysuspended from the ceiling of the compartment.

The vaporized ammonia leaves the evaporator 14 through conduit 15 andreturns to the heat exchanger 47. In addition to permitting heattransfer between the vaporized ammonia and the incoming liquid, the heatexchanger 47 also acts as an accumulator and permits separation of anyliquid which might have been entrained with the vaporized ammonia.

From the heat exchanger 47 the ammonia vapor flows through conduit 16,whichcontains a thermostatic throttling valve 17 which performs the samefunction as the thermostatic throttling valve 17 illustrated in FIGS. 1and 2. In fact, by employing a single solenoid valve which is responsiveto both the temperature within the refrigerated compartment and thetemperature of the vaporized ammonia leaving 7 the evaporator, a moresimplified refrigeration system is provided in those cases where mediumtemperature (35-45 F.) are to be maintained.

After passing through the thermostatic throttling valve 17, the ammoniavapor continues to flow through conduit 16 to the ammoniadissociator-burner 18, which is the same as the dissociator-burner 18illustrated in FIGS. 1 and 2 except instead of having electrical heatingelements as the means for initially heating the catalyst 27, thedissociator-burner 18 has a burner unit 51 which is connected to asource of liquefied petroleum gas 52. The burner unit 49 is situatedsuch that the heat of combustion of the liquefied petroleum gas heatsthe catalyst 27 to a temperature at which ammonia is dissociated in thepresence of the catalyst.

In addition to providing the heat necessary to raise the temperature ofthe catalyst during start-up, the liquefied petroleum gas can also beused to maintain catalyst 27 and dissociator-burner 18 at the preferredoperating temperatures in the event the flow of ammonia is insufficientto do so. This is achieved by interposing between the burner unit 51 andthe source of LP gas 52 a solenoid valve 53 which is actuated by aswitch 54 which reacts to the pressure in the conduit 16 conveyingammonia vapor to the dissociator-burner 18. When the pressure fallsbelow the level corresponding to the minimum flow rate of ammoniarequired to maintain combustion, the switch 54 reacts to the lowerpressure and causes the solenoid valve 53 to open, thereby permitting LPgas to flow to the burner unit 51 where the gas is burned. In lieu ofbeing activated by the pressure in conduit 16, the solenoid valve 53 canbe activated by other indicia of insufficient rate of flow of ammonia,such as the temperature within the dissociator-burner l8.

Some or all of the vaporized ammonia can also be utilized to run aninternal combustion engine 55. Internal combustion engines utilizingundissociated ammonia as fuel have been developed and are described inpublications available to the general public from the US. Department ofCommerce (Clearinghouse for Scientific and Technical Information) underthe designations AD 624,565, AD 633,632, AD 633,633, and AD 634,68l.Internal combustion engines which ordinarily run on gasoline will runsatisfactorily on ammonia which has been dissociated such that itcontains from about 2.5 to about 10 percent by weight of hydrogen. Theoutput of the internal combustion engine 55 can be used to performuseful work, such as operating a hydraulic pump 56 which drives ahydraulic motor 57 connected to air circulating fan 59 in thecompartment being refrigerated. An electric generator (not shown) can besubstituted for the hydraulic pump 56 and motor 57. A gas turbine (notshown) may be substituted for the intemai combustion engine 55. Suitableammonia-fired gas turbines are described in U.S. Department of Commercepublication AD 657,585.

A refrigeration system substantially as illustrated in FIG. 3, exceptthat the internal combustion engine was connected to thedissociator-burner at the outlet of the catalyst tubes, was operatedunder conditions of low, moderate and high refrigeration loads based ontypical requirements for refrigerated trucks. The catalyst employed waspromoted iron supported on alumina and was obtained commercially fromGirdler, inc. under the designation G-47. The internal combustion enginewas a 10 hp Briggs and Stratton gasoline engine with carburetionmodified for fuel gas. The exhaust gases of the dissociator-burner andthe internal combustion engine were analyzed for undissociated ammoniaand oxides of nitrogen by scrubbing a measured volume of exhaust gasthrough an acidified aqueous solution of potassium permanganate toabsorb ammonia and to oxidize nitric oxide and nitric dioxide tonitrate. The scrubber solution was then analyzed for ammonia andnitrate. The results are tabulated below.

27. After being partially dissociated in the section containing thecatalyst, the ammonia enters the burner section 26C. The burner section26C contains a plurality of apertures 28 through which the partiallydissociated ammonia is discharged. Upon being discharged, the partiallydissociated ammonia is combusted in the presence of air such that theheat of combustion maintains the catalyst 27 at a temperature at whichammonia is dissociated in the presence of catalyst. In order to conservesufficient heat of combustion to maintain the catalyst 27 at suchtemperature, the conduit 26 is contained within an insulated housing 29.

sociator-burner where the undissociated ammonia is readily combusted.The flow of excess ammonia is diverted by a bypass valve 39, which maybe a v diaphragm actuated differential valve which opens on rise inpressure above a set point.

Although the refrigeration system of this invention has been describedwith particular reference to the refrigeration of trucks, the system canalso be used to provide refrigeration in similar manner for othertransport vehicles, such as railway cars and ships, and also forstationary locations. For example, the refrigeration system of thisinvention can be used to provide emergency or standby refrigeration incase of power failure or mechanical failure in the main system.Similarly, the system can be used to provide auxiliary refrigerationduring periods of peak refrigeration requirements, such as occurs duringespecially hot summer days. In analogous manner, the refrigerationsystem can be used Ammonia Ammonia pressure to consump- Un-Refrigeradissociator, tion, Engine Sampling Oxides of dissociated tioninches of pounds operating period, nitrogen, ammonia,

Run number Stream analyzed conditions water per hour conditions minutesp.p.m. p.p.p.

1 Dissoeiator-bnrner cxhaust.. Low 8 3-6 on 34 49 2 ..do oderate.. 1510-14 Ofi.. 33 35 3 .-do High 30-00 20-30 011 34 97 153 4 Engineexhaust" Moderate. 15 10-14 No load 30 194 126 do, "do... 15 10-14Loaded. 34 1, 1, 250 d Hig 30-45 20-30 No load." 33 357 438 27-35 20-30Loaded- 30 1, 163 637 The above runs illustrate typical operatingconditions for an average (30 foot) refrigerated truck and 55 as thesole source of refrigeration where refrigeration is required for only ashort period of time each year. For example, requiring no externalsource of power, the refrigeration system of this invention can be usedin the field to provide quick refrigeration of fresh perishableproducts, such as berries, salmon or other fruit or fish, which are onlyavailable during short seasons.

1 claim:

1. A refrigeration system comprising:

a. a storage tank for liquid ammonia,

b. an evaporator wherein the liquid ammonia is vaporized by absorbingheat from the surroundings of the evaporator,

c. a conduit for conveying liquid ammonia from the storage tank to theevaporator,

d. means for combusting the vaporized ammonia wherein a more flammablegas is added to the ammonia to improve combustibility,

e. a conduit for conveying the vaporized ammonia from the evaporator tothe means for combusting the vaporized ammonia, and

f. means for regulating the flow of ammonia through the refrigerationsystem.

2. The refrigeration system of claim 1 wherein the means for combustingthe vaporized ammonia is an ammonia dissociator-burner comprising,within an insulated housing defining a combustion chamber, a conduitcontaining a catalyst for partially dissociating the vaporized ammoniaand having an aperture permitting discharge andcombustion of thepartially dissociated ammonia such that the heat of combustion maintainsthe catalyst at a temperature at which ammonia is dissociated in thepresence of the catalyst.

3. The refrigeration system of claim 2 which includes that required tomaintain the dissociator-burner at optimum operating temperatures fromthe conduit containing the catalyst to a conduit leading directly to thecombustion chamber without contacting the catalyst, whereby the excessammonia is burned directly with the partially dissociated ammonia.

4. The refrigeration system of claim 3 which includes a conduit forbleeding accumulated water from the evaporator.

5. The refrigeration system of claim 4 wherein the means for regulatingthe flow of ammonia comprises a surge tank interposed between theevaporator and the storage tank such that the liquid ammonia flows underautogenous pressure from the storage tank to the surge tank and bygravity from the surge tank to the evaporator, the surge tank havingmeans for regulating the level of liquid ammonia therein.

6. The refrigeration system of claimS wherein the means for regulatingthe flow of ammonia includes a thermostatic throttling valve interposedbetween the evaporator and the dissociator-burner, whereby thethermostatic throttling valve adjusts the pressure of the ammonia in theevaporator in response to the refrigeration demands placed on thesystem.

7. The refrigeration system of claim 6 including means for initiallyheating the ammonia dissociation catalyst to a temperature at whichammonia is dissociated in the presence of the catalyst.

8. The refrigeration system of claim 7 wherein the means for initiallyheating the ammonia dissociation means for diverting vaporized ammoniain excess of catalyst comprises an electrical heating element.

9. The refrigeration system of claim 7 wherein the means for initiallyheating the ammonia dissociation catalyst comprises a burner unitconnected to a source of liquefied petroleum gas, the burner unit beingsituated such that the heat of combustion of the liquefied petroleum gasheats the ammonia dissociation catalyst to a temperature at whichammonia is dissociated in the presence of the catalyst.

10. In an open cycle refrigeration process for maintaining a compartmentat a selected temperature, comprising 1 a. providing a source of liquidammonia,

b. absorbing heat from the compartment by vaporizing the liquid ammoniawithin an evaporator,

c. regulating the flow of ammonia to maintain the compartment at theselected temperature, and d. disposing of the vaporized ammonia, theimprovement which comprises disposing of the vaporized ammonia byburning in the presence of a more flammable gas.

11. The process of claim 10 wherein the step of disposing of thevaporized ammonia comprises partially dissociating the vaporized ammoniaby passing it over an ammonia dissociation catalyst to generate at least2 percent by weight of hydrogen, and burning the partially dissociatedammonia such that the heat of combustion maintains the catalyst at atemperature at which ammonia is dissociated in the presence of thecatalyst.

12. The process of claim 11 wherein ammonia in excess of that requiredto maintain the catalyst at a temperature between l,200 F. and l,700 F.is burned directly with the partially dissociated ammonia.

13. The process of claim 12 including the step of continuously bleedingaccumulated water from the evaporator.

14. The process of claim 13 including the step of combining theaccumulated water with the vaporized

2. The refrigeration system of claim 1 wherein the means for combustingthe vaporized ammonia is an ammonia dissociator-burner comprising,within an insulated housing defining a combustion chamber, a conduitcontaining a catalyst for partially dissociating the vaporized ammoniaand having an aperture permitting discharge and combustion of thepartially dissociated ammonia such that the heat of combustion maintainsthe catalyst at a temperature at which ammonia is dissociated in thepresence of the catalyst.
 3. The refrigeration system of claim 2 whichincludes means for diverting vaporized ammonia in excess of thatrequired to maintain the dissociator-burner at optimum operatingtemperatures from the conduit containing the catalyst to a conduitleading directly to the combustion chamber without contacting thecatalyst, whereby the excess ammonia is burned directly with thepartially dissociated ammonia.
 4. The refrigeration system of claim 3which includes a conduit for bleeding accumulated water from theevaporator.
 5. The refrigeration system of claim 4 wherein the means forregulating the flow of ammonia comprises a surge tank interposed betweenthe evaporator and the storage tank such that the liquid ammonia flowsunder autogenous pressure from the storage tank to the surge tank and bygravity from the surge tank to the evaporator, the surge tank havingmeans for regulating the level of liquid ammonia therein.
 6. Therefrigeration system of claim 5 wherein the means for regulating theflow of ammonia includes a thermostatic throttling valve interposedbetween the evaporator and the dissociator-burner, whereby thethermostatic throttling valve adjusts the pressure of the ammonia in theevaporator in response to the refrigeration demAnds placed on thesystem.
 7. The refrigeration system of claim 6 including means forinitially heating the ammonia dissociation catalyst to a temperature atwhich ammonia is dissociated in the presence of the catalyst.
 8. Therefrigeration system of claim 7 wherein the means for initially heatingthe ammonia dissociation catalyst comprises an electrical heatingelement.
 9. The refrigeration system of claim 7 wherein the means forinitially heating the ammonia dissociation catalyst comprises a burnerunit connected to a source of liquefied petroleum gas, the burner unitbeing situated such that the heat of combustion of the liquefiedpetroleum gas heats the ammonia dissociation catalyst to a temperatureat which ammonia is dissociated in the presence of the catalyst.
 10. Inan open cycle refrigeration process for maintaining a compartment at aselected temperature, comprising a. providing a source of liquidammonia, b. absorbing heat from the compartment by vaporizing the liquidammonia within an evaporator, c. regulating the flow of ammonia tomaintain the compartment at the selected temperature, and d. disposingof the vaporized ammonia, the improvement which comprises disposing ofthe vaporized ammonia by burning in the presence of a more flammablegas.
 11. The process of claim 10 wherein the step of disposing of thevaporized ammonia comprises partially dissociating the vaporized ammoniaby passing it over an ammonia dissociation catalyst to generate at least2 percent by weight of hydrogen, and burning the partially dissociatedammonia such that the heat of combustion maintains the catalyst at atemperature at which ammonia is dissociated in the presence of thecatalyst.
 12. The process of claim 11 wherein ammonia in excess of thatrequired to maintain the catalyst at a temperature between 1, 200* F.and 1,700* F. is burned directly with the partially dissociated ammonia.13. The process of claim 12 including the step of continuously bleedingaccumulated water from the evaporator.
 14. The process of claim 13including the step of combining the accumulated water with the vaporizedammonia.
 15. The process of claim 14 including the step of utilizing thevaporized ammonia as fuel to run an internal combustion engine or a gasturbine.
 16. The refrigeration system of claim 1 wherein the moreflammable gas is hydrogen generated by partial dissociation of thevaporized ammonia.
 17. The process of claim 10 wherein the moreflammable gas is hydrogen generated by partial dissociation of thevaporized ammonia.